1. Field of the Invention
The present invention relates to an exposure device and exposure method which transfer a pattern formed on a mask or reticle onto a substrate such as a wafer, and also to a device manufacturing method for manufacturing semiconductor devices, liquid crystal display devices, image pickup devices, thin-film magnetic heads, and other devices using the exposure device and exposure method.
2. Description of Related Art
In a photolithographic step, which is one of the steps for manufacturing semiconductor devices, liquid crystal display devices, image pickup devices, thin-film magnetic heads, and other devices, an exposure device is used that transfers a pattern that is formed on a mask or reticle (hereinafter, when referring to these generically, they will be referred to as masks) onto a wafer or glass or the like (hereinafter, when referring to these generically, they will be referred to as substrates) on which a photosensitive agent such as photoresist has been coated.
In recent years, step-and-repeat types of exposure device, for example, reduction projection types exposure device (what are known as steppers) or step-and-scan types exposure device are widely used. These step-and-repeat types exposure device are apparatuses that hold a substrate on a stage that is able to move freely two-dimensionally, and by moving the substrate in steps using this stage, repeatedly perform an operation in which a pattern image on a article is sequentially exposed onto each shot area on a substrate such as a wafer. The aforementioned step-and-scan types exposure device are apparatuses that, when transferring a pattern on a reticle onto a predetermined shot area on a wafer, sequentially transfer the pattern formed on the reticle onto the shot area while moving the reticle and wafer in synchronization.
In recent years, among the aforementioned devices, there have been considerable advances, in particular, in the further integration of semiconductor devices and, for example, process rules have become extremely minute at approximately 0.13 μm. As a result, exposure devices have achieved an improvement in resolution, and an improvement in the positioning accuracy of the pattern image on the reticle that is projected via a projection optical system relative onto the shot area of the wafer. Specifically, in order to improve the resolution, for example, a wavelength reduction in the wavelength of the exposure light and a high numerical aperture (NA) in the projection optical system have been achieved, while in order to improve positioning accuracy, for example, precise and rigorous control of the baseline amount is conducted.
The baseline amount is the distance between a reference point (for example, the center of the projection) of the pattern image on the reticle that is projected onto the wafer and a reference point (for example, the center of the measured field of vision) of an off-axis type of alignment sensor. In order to measure alignment marks that are formed on a wafer, a variety of alignment sensors are provided in an exposure device, and one of these is an off-axis type of alignment sensor that is placed in the vicinity of a side portion of a projection optical system. If this type of alignment sensor is used, a position that is obtained by correcting the result of a measurement by the alignment sensor using the baseline amount becomes the position where each shot area is located during an exposure. Accordingly, by accurately controlling the baseline amount, it is possible to achieve an improvement in the accuracy with which the projected pattern is superimposed on the shot area.
In the manufacture of devices in recent years, because there has been a demand for an improvement in productivity, there is a need to improve throughput, namely, to improve the number of wafers that are processed in a unit time. In order to improve throughput, in a step-and-repeat type exposure device, by raising the rate of acceleration of the wafer stage, a reduction in the time required for acceleration and deceleration is achieved. In a step-and-scan type exposure device, in addition to improving the acceleration and deceleration of the wafer stage and the reticle stage, by improving the scanning speed of the wafer stage and reticle stage during exposure, a reduction in the time required for exposure is achieved.
However, in order to improve throughput, if the rate of acceleration of the wafer stage or reticle stage is improved and acceleration and deceleration is frequently repeated, the quality of heat generated by the motor that drives the wafer stage or by the motor that drives the reticle stage is increased. Because these motors are provided inside the exposure device, each time an exposure operation is repeated there is a large variation in the temperature inside the exposure device. In a step-and-scan type exposure device, in particular, because both the wafer stage and the reticle stage are driven by motors during an exposure (i.e., during the transfer of a pattern), the rate of temperature change is considerable. A change in temperature is generated inside the exposure device not only by the motors provided in the wafer stage and reticle stage, but also when drive systems (for example, the lens drive system of the projection optical system and the reticle blind drive system) inside the exposure device are driven.
If the temperature inside the exposure device changes, a change (for example, a change in the best focus position and a change in aberration) is generated in the optical characteristics of the projection optical system. As a result, deterioration in the resolution and the like occurs and problems arise when a detailed pattern is being transferred. Moreover, because thermal expansion and thermal deformation are generated in the alignment sensors and the stages by changes in temperature inside the exposure device, there is a concern that a variation in the baseline amount (i.e., baseline drift) will occur during exposure. Because of this, the problem arises that a deterioration in accuracy occurs when the projected pattern and the shot area are overlayed. In addition, the temperature of the atmosphere surrounding the stages is raised by the heat generated by the stages, and the problem arises that the stage positioning accuracy is worsened by the effects such as fluctuations in the optical path of the interferometer that measures the positions of the stages.
Accordingly, in order to prevent reductions in the resolution, reductions in the accuracy of the overlay, and reductions in the stage positioning accuracy, it is necessary to maintain a constant temperature inside the exposure device. Because of this, conventional exposure devices are provided with a temperature sensor that detects the temperature inside the exposure device and with a temperature control device, and, based on detection results from the temperature sensor, the temperature control device conducts feedback control so as to maintain a constant temperature inside the exposure device. Either air-cooled or liquid-cooled temperature control devices may be used as this temperature control device, however, commonly, exposure devices are provided with liquid-cooled types of temperature control device as these have an excellent cooling performance.
However, using as an example an exposure device that is provided with, for example, a liquid-cooled type of temperature control device, the diameter of pipes that are used to conduct temperature-controlled coolant in the vicinity of a heat generating source such as a motor is restricted by the size of the exposure device and by space limitations inside the exposure device. Moreover, because it is clearly not possible to use any optional component as a pipe, the pressure inside the pipes is restricted and the flow rate is also limited. Furthermore, in order to perform temperature control, it is desirable that the temperature control apparatus be located extremely close to the heat generating source, however, it is not always possible to employ this type of structure due to the structure limitations of the apparatus. Accordingly, due to the restrictions of this type of apparatus structure, there is an increase in time wastage due to control.
In order for exposure devices of recent years to provide the expected performance, for example, the temperature of the wafer stage and reticle stage must be controlled within a range of approximately 1/10° C., and the temperature of the projection optical stem must be controlled within a range of approximately 1/100° C. However, if the aforementioned time wastage is considerable, then in a conventional temperature control device that only uses feedback control, it is difficult to conduct this type of high precision temperature control. Moreover, in recent years, wafer stages and reticle stages have had to increase in size to keep pace with the increase in size of wafer diameters, so that the heat capacity thereof has increased as has the thermal time constant. Furthermore, because the ability to drive the reticle stage and wafer stage at high speed is more and more in demand in order to improve throughput, the quantity of heat generated by the motors that drive the reticle stage and wafer stage is also increasing, and highly accurate temperature control in the above described temperature range has become more difficult.
It is an aim of the present invention to provide an exposure device and exposure method as well as a device manufacturing method that uses this exposure device and exposure method that result in it being possible to improve device manufacturing efficiency by maintaining the performance of an exposure device consistently at the expected performance, by performing temperature control inside the exposure device with a high degree of accuracy even if time wastage due to control does occur.